The present invention relates to a laminate and an article such as roll-up sign, pavement marking tape and other retroreflective articles, comprising a retroreflective layer and a tear resistant film layer.
U.S. Pat. Nos. 5,591,530 and 5,422,189 relate to a flexible optically uniform sign face substrate comprising at least one layer of durable thermoplastic sheeting and an optically uniform dimensionally stable scrim film, and more particularly a sign face substrate comprising at least one layer of optically uniform dimensionally stable multilayer scrim film laminated between at least two layers of durable thermoplastic sheeting for use in areas such as awning, canopy, fascia or sign material construction. The scrim film preferably comprises alternate layers of a stiff polyester or copolyester and a ductile thermoplastic polymeric material wherein the polyester or copolyester has a tensile modulus greater than 200 kpsi and the ductile material has a tensile modulus of less than 200 kpsi and a tensile elongation of greater than 50%. The sign face substrate is clear, transparent or translucent and does not show a visible pattern when backlit. In the xe2x80x9cBackground of the Inventionxe2x80x9d of these references, the scrim film is described as being advantageous with respect to polyester woven scrim construction that can introduce defects during the weaving process and final construction of the woven scrim, such as extraneous threads that are visibly apparent when the sign face is backlit. Further, woven scrim is also described as being susceptible to wicking, which can lead to growth of mold and mildew. The scrim film is also advantageous with regard to channel cut sign face construction prepared from rigid acrylics that are subject to cracking, shattering, and crazing. The sign faces are attached to a housing equipped with a lighting source to produce rigid backlit sign.
U.S. Pat. No. 4,544,586 relates to laminar structures useful as road sign, markers, informational signs and the like comprised of (i) a modified thermoplastic polyester core structure; and (ii) a front reflective layer disposed on and laminated to said core structure. At column 5, lines 52+this reference states that, xe2x80x9cPreferably, the core structure A has a thickness in the range of from about 60 to about 250 mils. In general, if the thickness of the core A is less than about 60 mils, the laminar structures of the instant invention do not exhibit sufficient rigidity to perform satisfactorily as a road sign or marker or informational sign, and the like, particularly if it is relatively large, e.g. 12 inches by 18 inches and larger. If the core structure is less than about 60 mils thick, i.e., from about 30 to 60 mils thick, it is still possible to utilize laminar structures as road sign, markers, informational signs, and the like. In such instances it is preferred to use these laminar structures in conjunction with appropriate mounting or supporting devices. These mounting or support devices act to provide stiffening support to the laminar structure and impart the requisite rigidity. Some illustrative non-limiting examples of particularly useful mounting or support devices are disclosed in U.S. Pat. Nos. 3,894,707; 4,066,233; 4,094,487; 4,125,240 and 4,211,381.xe2x80x9d The mounting or support devices described therein are for securing an object, such as a sign, to a body, such as a post. The exemplified modified polyester sheet exhibits no permanent deformation (under the described conditions) in comparison to an aluminum sheet. Hence, one of ordinary skill in the art would conclude that the laminar is relatively stiff and rigid, comparable to that of aluminum sheeting used for sign substrate.
Typical constructions for pavement marking sheet materials are known from U.S. Pat. Nos. 4,117,192 and 4,299,874, for example. Such materials typically include a base sheet comprising elastomer precursors, i.e., ingredients that may be vulcanized or cured to form an elastomer. Retroreflective elements, such as glass microspheres in addition to skid-resisting particles are partially embedded in a support film on the surface of the base film. A pressure sensitive adhesive is typically present on the opposing surface the base sheet. The base sheet also typically comprises fibrous scrim.
Roll-up signs are known in the outdoor display and traffic control materials art. Such signs are portable and can be folded or rolled up for transport and storage. Typical constructions for roll-up signs are known from U.S. Pat. No. 6,004,422, for example. The article comprises a microstructured member such as highly flexible cube corner type retroreflective sheeting, a sealing layer, and a backing layer comprising a fibrous web (e.g. woven scrim) to provide the desired tear strength. During use, the signs are typically attached to a collapsible supporting apparatus to allow the sign to be displayed along a roadway. The roll-up signs typically include corner pockets that receive diagonally extending cross arms of a collapsible stand. Over time, roll-up signs can crack and tear, particularly along the circumference of an interface between a rigid corner pocket element and the flexible sign or where sewn pockets are formed.
The present Applicant has found that tear resistant films can be employed in roll-up signs, as well as other retroreflective laminates and articles. In a preferred embodiment, the tear resistant film is disposed on the retroreflective viewing surface of the laminate or article. Surprisingly, in doing so, the scrim as well as other layers such as the protective top film can be eliminated.
The present invention is a laminate comprising a retroreflective layer having a retroreflective viewing surface and a tear resistant film disposed on the retroreflective layer. The tear resistance film which has a nominal thickness of x in microns, preferably has a Graves area in at least one direction of at least about 40+0.4(x) kpsi % (275+2.76(x) MPa %). The Graves elongation at break is preferably at least 20%, and more preferably at least 40%. Further, the laminate exhibits a Graves area of at least 60 kg %. The tear resistant film preferably has a tensile modulus of at least 120 kpsi (828 MPa) in at least one direction. More preferably, the tensile modulus is at least 150 kpsi (1,035 MPa), even more preferably at least about 240 kpsi (1,656 MPa) and most preferably at least about 450 kpsi (3,105 MPa) in at least one direction.
The laminate is preferably substantially free of fibrous scrim. The tear resistant film and retroreflective layer are bonded directly to each other or bonded indirectly by means of one of more intermediate layers. The laminate preferably exhibits a 90 degree peel strength of at least 0.5 lb f/in (0.9 Newtons/cm).
In another embodiment, the present invention is a retroreflective article that is preferably flexible such that it can be wrapped by hand around a mandrel having a diameter of about xc2xdxe2x80x3 (1.3 cm) at 25xc2x0 C. without cracking. Representative articles include roll-up signs, flags, banners, cone wrap sheeting, post wrap sheeting, barrel wrap sheeting, license plate sheeting, barricade sheeting, sign sheeting, vehicle marking sheeting, segmented vehicle marking sheeting, pavement marking tapes and sheeting; retroreflective tapes and decals; sew-on retroreflective articles, and the like.
In preferred embodiments the tear resistant film is transparent and is disposed on the retroreflective viewing surface of the laminate. The tear resistant film preferably comprises one or more light stabilizing compounds, one or more ultraviolet light absorbing compounds, and mixtures thereof.
In another embodiment the present invention is a laminate comprising a retroreflective layer and a tear resistant film disposed on the retroreflective layer; wherein the tear resistant film is a multilayer film. The multilayer film preferably comprises a surface comprising a thermoplastic polymeric material that is bonded directly to the retroreflective layer. The thermoplastic polymeric material preferably comprises co-polyethylene terephthalate. The multilayer tear resistant film preferably comprises alternate layers of a stiff polyester or copolyester and a ductile thermoplastic polymer wherein the polyester or copolyester has a tensile modulus greater than 200 kpsi (1380 MPa) and the ductile material has a tensile modulus of less than 200 kpsi and a tensile elongation of greater than 50%. For embodiments wherein a single multilayer film is employed, the multilayer film preferably comprises a total of more than five stiff and ductile layers situated one on the other in a parallel array, the stiff layer having an average nominal thickness of greater than about 1 micron.
The retroreflective laminate may further comprise at least one tie layer disposed between said retroreflective layer and said tear resistant film and/or at least one backing layer.
In another embodiment the present invention is a laminate comprising a retroreflective layer and a tear resistant film, wherein said laminate is substantially free of fibrous scrim and wherein the Graves area of the laminate is at least 150 kg %.